Recently my friend, lets just call him "S", appeared in court charged with dangerous driving, a very stressful situation particularly as he chose to defend himself (ignoring the famous saying, by lawyers, that anyone who chooses to defend themselves in court has an idiot for a client). On an icy day in January 2020, S was driving on the outskirts of Kitchener when he braked to avoid a squirrel on a long icy patch or doad and skidded for thirty meters, only stopping when he hit a lamp post (there was no curb). A motorist who was heading in the other direction saw the accident and didn't bother to stop to see if S was OK, but did later appear in court as a witness for the prosecution, testifying that S was speeding (at more than 50km/h). The prosecution used some physics (yet to be covered in the course), to determine from the damage done to the lamp post (and the fact that S was unhurt), that the car was traveling at 30km/h just before the impact. Using Newtons laws and the accepted values for the coefficients of static and kinetic friction between this kind of ice and rubber (0.5 and 0.4 respectively), they demonstrated that S was traveling at a high speed (over 60km/h) when he applied the breaks. S however using the same values pointed out that the road had a small but important slope downwards toward the lamppost, of thirteen degrees and was able to show that his initial speed was therefore substantially lower and below the speed limit of 50km/h. S was found not guilty.

Use Newtons laws and kinematics to explain the calculations of the prosecution and S, keep everything on one slide. The idea behind one slide, is to let the viewer see all parts of the solution at once and follow the logic, so please don't introduce and extract the physical properties on the introduction slide to get extra space, this will be marked down. You don't have to include the long text of the question in the solution but you should verbally explain where each physical property extracted, comes from in the question. As usual keep the presentation to five minutes, and include discussion about assumptions or difficulties at the end, use a pointer, turn on your video and only submit a video file. The rubric will be the same as last time, so please print it out so that you can easily read it.

As an introduction to the topic, on one slide only, please explain how and when static and kinetic friction apply to a car wheel in contact with the road, and how it is similar or different to a foot making contact with the ground when walking.